1. Field of the Invention
The present invention relates to testing of pipes and, in particular, to a plug system for restricting the water flow through a pipe.
2. Description of Related Art
Pipes that carry water and other liquids are prone to wear and damage. Sewer pipes, for example, may be prone to intrusion by tree roots or damage by ground movement. Testing can be routinely performed on the pipes in order to ascertain if the pipe is damaged and leaking. Additionally, testing may be performed on pipes to locate leaks in order to facilitate repairs.
One method for testing pipes is with the use of a Focused Electrode Leak Locater (FELL) system. The FELL system locates defects by checking the electrical continuity through the walls of a pipe. Most sewer pipes consist of electrically insulating materials; however, a defect in the pipe that leaks sewage or other electrically conductive liquids will also leak electrical current. For a constant applied voltage, the larger the defect in the pipe wall, the greater the electrical current that will pass through it. A FELL test is carried out by pulling an electrode, called a sonde, through the pipe and measuring the variation of electric current flow through the wall of the pipe, then through the ground to an electrode on the surface. The electrode on the surface can be a metal stake driven into the ground. The sonde may be specially constructed such that the electric current only flows through the pipe radially from a narrow band located at the center of the sonde. The sonde may also contain a microprocessor that controls the voltage applied to the sonde, measures the current flow through defects in the pipe wall, records the position of the sonde in the pipe and discloses the data to a user. The resulting data may be displayed as, for example, a trace of current versus sonde position.
A usual requirement of FELL testing is that the pipe be full of water in the immediate vicinity of the sonde to provide electrical contact between the sonde and the pipe wall. At present, this requires that the pipe section to be tested be blocked just outside of an access port or manhole downstream from the test section. Once the section of pipe to be tested is isolated in this fashion, the isolated section is completely filled with water (surcharged), until the upstream end of the crown of the pipe section to be tested is covered with water. This may also involve blocking the upstream end of the test section just above another access port. In some cases, access ports may be separated by several tens of meters, for example 100 m.
Surcharging a pipe can cause backflow into residences and is considered an unwarranted risk by sewer maintenance supervisors. A significant percentage of sewer pipe section cannot be FELL tested using this method to fill the pipe sections with water because they have a high gradient (i.e., deviation from the horizontal) and cannot be fully surcharged because the top of the downstream manhole may be lower than the crown of the pipe at the upstream manhole. In addition, surcharging the pipe consumes a lot of time, in some instances more than half of the time required to carry out the test.
Presently FELL testing is carried out by stringing a haul line between manholes of the pipe section to be tested, pulling the FELL sonde through the pipe with the haul line from one manhole to the next, filling the test section with water, activating the sonde recording system, pulling the sonde back to the entry manhole while recording the variation of the current flow through the walls of the pipe, and emptying the sewer pipe. From 70% to 90% of the time to carry out a FELL test is occupied stringing the haul line and filling and emptying the sewer.
Another sewer pipe maintenance operation is water jet cleaning. Sewer pipe water jet cleaning is carried out by inserting a hose into a sewer pipe at a manhole and pumping water through the hose at high pressure. The nozzle at the end of the hose produces high pressure jets of water that clean the pipe and propel the hose end through the pipe. The process is usually carried out in the upstream direction between two manholes. Once the nozzle reaches the upstream manhole the hose is retracted from the pipe.
There are further additional operations that are routinely performed on pipes (sewage or otherwise) where blockage of the pipe, at least temporarily, is required. Therefore, there is a need for methods of blocking a pipe in order to perform operations in the pipe in a quick and efficient manner.